Generally, the light sources of conventional luminaires usually can be sorted into two categories, which are point sources such as incandescent bulb and energy-saving fluorescent bulb, and line source such as fluorescent tube. These two types of light source are all capable of discharging light beams in a radiation manner. However, as the sizes of these two light sources are considered too large while comparing with that of light emitting diode (LED), LED has been intensely studied and becoming the main trend of future luminaires as the luminous efficiency of LEDs is enhancing continuously and unceasingly. Since LED is considered to be a flat light source as it can only discharge light beams through the light emitting surface thereof, it can only provide a limited angle of light and thus most LED luminaires are adopting either bottom-lighting module or reflective module. In addition, as the brightness of a single LED currently available is still not sufficient to be used as the sole and only light source of modern luminaires, a plurality of LEDs are clustered into a lighting module for proving sufficient luminance.
Please refer to FIG. 1, which is a bottom-lighting LED luminaire disclosed in U.S. Pat. No. 6,502,956, entitled “Light emitting diode lamp with individual LED lenses”. Although the bottom-lighting LED luminaire of FIG. 1 has a plurality of LEDs 14 arranged on a printed circuit board (PCB) 10 that the luminance is enhanced, it is prone to cause severe glare causing discomfort to viewers. Furthermore, if any individual LED or portion of the plural LEDs is damaged, the damaged LEDs are visible and apparent.
Please refer to FIG. 2, which is an illumination system for use with machine vision systems disclosed in U.S. Pat. No. 6,871,993, entitled “Integrating LED illumination system for machine vision systems”. The illumination system is specifically adapted to be used in optical and barcode scanning systems for focusing light on a line or area in which a machine vision system collects image data. As seen in FIG. 2, the illumination system comprises a reflector 12 and an LED array 14. The reflector 12 includes a focusing reflective surface 13 that is concave in shape. An elliptical cross-sectional shape is preferred, but other shapes, such as parabolic and hyperbolic could be used, for example. The LED array 14 comprises a substrate 26 and a plurality of LEDs 16 mounted on the substrate 26. Each of the plurality of LEDs is positioned in the focal region of the reflector 12 while enabling the same to emit light toward the focusing reflective surface 13. As the primary objective of thus illumination system is to focus light emitted from the plural LEDs 16 toward the illumination area, that it is suitable to be applied in barcode scanning system, but not suitable to be used as luminaire.
Please refer to FIG. 3, which is an illuminating device for use as a headlamp disclosed in U.S. Pat. No. 5,136,483, entitled “Illuminating device”. The illuminating device of FIG. 3 is comprised of: a reflecting screen 16; a plurality of LEDs, being fitted flatly onto the circumferential edge of the reflecting screen 16; and a plurality of heat dissipating fins 19; wherein the light emitting from each LED 14 is reflected by the inwardly concave reflecting screen 16 and thus being discharged out of the illuminating device parallelly. As each of the plural LEDs 14 is arranged flatly on the circumferential edge of the reflecting screen 16, only a portion of light emitted therefrom within a specific angle can be reflected by the reflecting screen 16 and discharged out of the illuminating device parallelly, while some other light emitted therefrom not within such specific angle are reflected and discharged in a scattering manner and even some other light emitted therefrom not within such specific angle are reflected inside the reflecting screen 16 repetitively without being discharged. As the result, not only the luminance of the illuminating device is adversely affected, but also no highly collimated parallel light beams can be discharged out of the illuminating device. Although the forgoing shortcomings can be overcome by improving the design of the reflecting screen 16, it is highly difficult to implement and, in particular, would introduce not much improvement.
Please refer to FIG. 4, which is a lamp disclosed in U.S. Pat. No. 5,838,247, entitled “Solid state lighting system”. The lamp 40 of FIG. 4 is comprised of: an inclined array of LEDs 12; and a reflector 44 inclined at a complementary angle A. It will be understood that the array may be the inverse, i.e. convergently inclined; and conical or pyrimidal. The angle of convergence or divergence may vary, with the angle of the reflector 44 correspondingly selected to achieve the desired direction and type (e.g. focussed or diffused) of light output, and thus to direct the light parallel to the polar axis 36 of lamp 40. Nevertheless, the lamp 40 is still short in that as the reflector 44 is a planar surface which can not match perfectly with the light emitting angles of those LEDs 12, not all the light reflected by the reflector 44 can be discharged parallel to the polar axis 36. Furthermore, since the reflector 44 is inclined, a comparatively large amount of LEDs 12 are required for illuminating similar luminance so that not only the lamp 40 is costly and not power-saving, but also it is bulky and has no surprising appearance.